Regulating valve features and characteristics Term: Spring Setting range: Regulating valve actuator spring adjustment range to balance the actual process force. Circulation capacity: the rated flow through the valve under the specified conditions. Clearance flow: The flow below the minimum controllable flow rate when the shut-off element is not seated. Diaphragm pressure range: diaphragm pressure range of high and low value of the difference. This can be considered as an inherent or installation feature. Double-acting actuator: An actuator that can be powered in either direction. Dynamic unbalance force: Due to the pressure of the process fluid, the active area is created on the spool at any given opening: in a membrane actuator, the effective area is the area of ​​the diaphragm that effectively produces the output force. The effective area of ​​the diaphragm may change as it moves, usually at the beginning of the stroke and at the end of the stroke. Molded diaphragms have a smaller effective area change than flat diaphragms, so molded diaphragms are recommended. Loss of gas - Off: A condition where the valve shutoff element is moved to the closed position when the drive energy is lost. Loss of gas - Open: a state where the valve shutoff element is moved to the open position when the drive energy is lost. Loss of Gas - Safety: A feature of the valve and its actuator that when actuated energy supply is interrupted, the valve shut-off element is moved fully closed, fully open, or left in the last position, either position being considered Is necessary to protect the process. Fail-safe mode of operation may require the use of auxiliary controls connected to the actuator. Flow characteristics: The relationship between the flow through the valve and the percentage of the rated stroke when the percentage of rated travel changes from 0 to 100%. This term should always be expressed as an inherent flow characteristic or an installation flow characteristic. Flow coefficient (Cv value): A constant (Cv value) for a given stroke that is related to the geometry of the valve and is used to measure flow capacity. It is the U.S. gallon of water at 60 ° F flowing through the valve at a pressure drop of pounds per square inch. High Pressure Recovery Valve: A valve construction that disperses relatively little fluid energy due to the streamlined internal profile and minimal fluid turbulence. As a result, the pressure downstream of the valve's retracted section returns to a very high percentage of the inlet pressure. Direct-flow valves, such as rotary ball valves, are typical high pressure recovery valves. Inherent Die Pressure Range: High and low pressure acting on the diaphragm to create a nominal spool stroke at atmospheric pressure. This range usually refers to the spring setpoint range, because when the valve is set in the working range, this range will be the valve range of motion. Inherent flow characteristics: The relationship between the flow and the closure element stroke as the valve moves from the closed position to the rated stroke when the pressure drop across the valve is constant. Installation Diaphragm Pressure Range: High and low pressure applied to the diaphragm to produce a nominal spool stroke under the valve body's specified operating conditions. Due to the forces acting on the shut-off element, the inherent diaphragm pressure range may differ from the diaphragm pressure range. Installation Flow Characteristics: The relationship between flow and shut-off element as the pressure drop across the valve is affected by changing process conditions as the valve moves from the closed position to the rated stroke. Low pressure recovery valve: A valve structure that disperses a large portion of the fluid energy due to turbulence created by the fluid channel profile. As a result, the pressure downstream of the systolic section of the valve returns to a lower inlet pressure percentage than the valve with more streamlined passages. Although each valve structure is not the same, ordinary straight-through valves often have low pressure recovery capabilities. Modified parabolic flow characteristics: A flow characteristic that provides equal percentage characteristics at the lower stroke of the shutoff element and linearity at the upper stroke of the shutoff element. Pushed down to close the structure: A through-type valve structure, the closure element is located between the actuator and the seat ring, so push rod actuator will move the closure element to the seat ring, and finally close the valve. The term can also be used for rotary valve construction. In rotary valve construction, the linear extension of the actuator stem moves the ball or disc toward the closed position. Also known as positive effect. Push down to open the structure: a straight-through valve structure. Its seat ring is located between the actuator and the shut-off element so that the push of the actuator releases the shut-off element from the valve seat, thus opening the valve. The term can also be used for rotary valve construction. In rotary valve construction, the linear extension of the actuator stem moves the ball or valve plate to the open position. (Also known as reaction). Adjustable ratio: The ratio between the maximum flow coefficient (Cv value) and the minimum flow coefficient (Cv value) when the deviation from the specified flow characteristics does not exceed the specified limits. A valve that is still well controlled has a 100: 1 adjustable ratio when the flow rate increases to 00 times the minimum controllable flow rate. Adjustable ratio can also be expressed as the ratio between the maximum and minimum controllable flow. Rated stroke: the valve closing element moves from the closed position to the rated full open position. Rated full open position is the maximum opening recommended by the manufacturer. Relative flow coefficient: The ratio between the flow coefficient (Cv value) at the specified stroke and the flow coefficient (Cv value) at the nominal stroke. Seat Leakage: The amount of fluid flowing through the valve when the valve is fully closed at the specified pressure differential and temperature o Spring Factor: Change in spring force per unit change in spring length. In diaphragm actuator valves, the spring constant is usually expressed in pounds per inch of compression. Stem Unbalanced Force: The net force generated on the stem at any position due to fluid pressure. Reduced flow section: the part with the largest flow velocity, the lowest hydrostatic pressure, and the smallest cross-sectional area. In a regulating valve, the converging section is usually located downstream of the actual physical limit. ANSI: American National Standards Institute abbreviation. API: American Petroleum Institute acronym. ASME: Abbreviation for American Society of Mechanical Engineers. ASTM: Abbreviation for American Society for Testing and Materials. Automatic Control System: A control system that can work without human intervention. Bode plots: logarithmic amplitude scale and phase angle plot of a transfer function on a logarithmic base. This is the most common form of graphically representing frequency response data. Calibration curve: A graphical representation of the calibration result. The steady state output of a device is expressed as a function of its steady state input. This curve is usually expressed as a percentage of the output span versus the percentage of the input span. Calibration cycle: Use the known value of the variable to be measured in the range of the meter in the ascent and descent direction, and record the corresponding output reading. The calibration cycle can be calibrated by first increasing and then decreasing the input of the device obtain. It is usually expressed as a percentage of the input range to the percentage of the input range. It provides a measure of hysteresis. Clearance flow: When the shut-off element is not seated, less than the minimum flow control that traffic. Controller: A device that automatically operates to adjust the controlled variable. Enthalpy: A thermodynamic quantity which is the sum of the internal energy of the valve body and its product of volume and pressure: H = U + pVo (also called heat capacity). Entropy: A theoretical measure of the energy that can not be converted into mechanical work in a thermodynamic system. Feedback signal: The return signal obtained by measuring the directly controlled variable. For a valve with a positioner, the feedback signal is usually a mechanical indication of the position of the connecting element of the shut-off element that feeds back to the positioner. FCI: Abbreviation for Fluid Control Organization. Frequency Response Characteristics: The frequency dependence of the steady-state sinusoidal input in amplitude and phase and the resulting basic sinusoidal output. The amplitude and phase shift of the output can be taken as a function of the input test frequency and used to describe the dynamic behavior of the control device. Hardness: The ability of a metal to resist plastic deformation, usually in the form of a depression. Plastics and rubber resist the ability of prongs to penetrate their surface. Oscillation: A type of vibration with a significant amplitude that still persists after the external stimulus disappears. Oscillation is sometimes referred to as a cycle or limit cycle. Oscillation is evidence of work at or near the stability limit. In regulating valves, instability of the control system or valve positioner can cause fluctuations in the actuator loading pressure, which can occur as a result. ISA: Abbreviation of American Society of Instrumentation. Now called the International Institute of Measurement and Control. Instrument Pressure: The output pressure provided by an automatic regulating valve to operate the valve. Loading pressure: The pressure used to position the pneumatic actuator. This is the actual pressure acting on the actuator diaphragm or piston. If the valve positioner is not used, the loading pressure can be gauge pressure. NACE: Used to represent the American Society of Corrosion Engineers. As the organization becomes more international in scope, the term has been changed to International NACE. NACE is no longer an acronym. 0SHA: Abbreviation for Occupational Safety and Health Act (USA). Working medium: This refers to the fluid, usually air or gas, used to power the work of valve positioners and automatic controllers. Work limit: A range of working conditions that a device can withstand without causing permanent damage to its working characteristics. Range: The area between two limits, the distance between which can be measured, accepted, or delivered, and is expressed as a range of values ​​(eg, 3 to 15 psi; -4 to 212 ° F; -40 to 100 ° C). Repeatability: In the entire range of travel, in the same direction, under the same operating conditions, for the same input